The main function of the skin is to provide a barrier for the transport of water and substances harmful to the body. The capability of a chemical substance to penetrate the skin often depends upon the composition of the carrier. When a drug or cosmetic is applied to the skin, some situations limit the rate of cutaneous permeation: first, the release of the active from the carrier and, secondly, the penetration of the latter through the skin barrier. Active ingredients in skin-care treatment pass into the skin through the pores of the pilose follicles, the canal of the tallow glands or through corneous extract.
The corneous extract is hygroscopic, in part due to the capability of preserving water of the keratin. The skin needs at least 10% of moisturizing by weight to keep its flexibility and softness. The association of intercellular lipids with the corneocytes of the corneous extract is crucial for keeping the barrier function and the capability of linking with water.
Substances favorable to the skin are water-soluble and oil-soluble. The capability of retaining water from the corneous extract may be restored by applying lipids selected for the corneous extract and in a suitable carrier. The size of the particles and their lipophilicity are main factors in the process of penetrating through the corneous extract. The molecules go through the membrane by both passive diffusion and active transport. The transport through the skin takes place primary by passive diffusion, which is governed by Fick's law. It determines that the base rate of diffusion or transport through the membrane is proportional to the difference in concentration of active on the two sides of the membrane.
Delivery systems play an important role in the development of effective skin-care products. Anti-aging treatments stimulate the growth of the skin-treatment market. Consumers expect rapid and visible results. In order to achieve these results, many companies are relying on advanced technology. Among the “delivery” technologies, there are systems of lipids, nanoparticles, microcapsules, polymers and films. These technologies are added in a carrier such as creams, liquids, gels and patches. The key aspects of the “delivery systems” are:                increasing/improving the penetration and improving the efficacy;        controlled delivery;        separating incompatible actives;        prolonging the shelf life/decreasing the degradation of active.        
Nanoparticles may be subdivided into two structure of encapsulated membrane: liposomes and nanoemulsions/nanosomes/nanotopes. Nanoemulsions differ from macroemulsions by their smaller size of oily particles, which are on the order of nanometers. Classic emulsions or macroemulsions have droplets in the size range of 1 to 20 micrometers, which impart to them the white or opaque aspect. Nanoemulsions have been characterized as being transparent or slightly translucent, depending on the particle size and on the difference in refraction index between oil phase and aqueous phase:
The nanoemulsion system may be applied in personal hygiene, pharmaceuticals, foods, household sanitary agents, agrochemicals and cosmetics.
The applicant indicates, hereinafter, the relevant documents of the prior art relating to the matter of the present invention.
Documents U.S. Pat. No. 6,274,150, BR 0000417, U.S. Pat. No. 6,464,990 and U.S. Pat. No. 6,413,527 describe a process for preparing a nanoemulsion based on phosphoric fatty acid esters. This process comprises mixing an aqueous phase and an oil phase with vigorous stirring at the temperature ranging from 10 to 80° C. to form a mixture, and homogenizing the mixture under high pressure raging from 600 bar to 1,800 bar, further carried out with a shear ranging from 2×166 s−1 to 5×108 s−1. Nanoemulsions present an average particle size ranging from 20 nm to 75 nm, for topical application.
On the other hand, document U.S. Pat. No. 5,994,414 describes a process for preparing an emulsion, which comprises forming a crude oil-in-water emulsion, which is subjected to homogenization under a pressure of about 900 to about 1,100 bar to obtain an average particle size of about 0.1 micron, with a maximal size of about 1 micron. The emulsion may be used in lotions for application onto the skin.
Document BR 0100335 describes oil-in-water nanoemulsions comprising particles with less than 150 nm for application in cosmetics, such as lotions and creams to be applied to the face and to the skin. In an embodiment of the invention, a process for preparing a nanoemulsion is described, which comprises mixing an oil phase and an aqueous phase by means of a homogenizer with a turbine, and then homogenizing with a homogenizer under high pressure, with 4 cycles, while keeping the temperature of the product below about 35° C.
Further, document BR 9705381 relates to the use of nanoemulsions on keratin fibers, comprising particles having an average size of less than 150 nm. These nanoemulsions are obtained by mixing an aqueous phase and an oil phase, under vigorous stirring, at a room temperature lower than 45° C., and then subjected to homogenization under high pressure.
Finally, document BR 9604724 describes an oil-in-water nanoemulsion comprising an average particle size smaller than 100 nm, intended for use on cosmetic and pharmaceutical products. The nanoemulsion may be prepared under a pressure ranging from 1,200 bar to 1,800 bar, and may present 7 cycles. The nanoemulsion may assume the form of a lotion or a gel.
All the documents cited above and still other documents of the prior art that deal with compositions and processes relating to nanoemulsion, considered less relevant for the present invention, do not disclose an oil-in-water nanoemulsion composition, be it for cosmetics or for pharmaceuticals, which exhibits an opaque coloration. Those skilled in the art know that, due to the reduced size of the oil particles dispersed in the aqueous phase, the coloration of the composition is transparent, varying, at most, to a bluish tone, as can be seen from the above-cited documents. In some of the above-listed documents, one can even see that attempts are made to achieve non-transparent nanoemulsions, by these attempts have failed in stability. In this regard, it is found that no teaching of the prior art proposes an oil-in-water composition comprising oily particles with a diameter on the order of nanometers, is stable for a period of 2 years and exhibits an opaque coloration. These characteristics and consequent advantages are comprised by the present invention and will be described hereinafter.